Benchmarking DFT Calculations for Adsorption Studies: Pharmaceuticals and Related Organic Molecules in Cation-Exchanged Zeolites

The choice of the exchange-correlation functional and dispersion correction significantly influences the adsorption energies obtained from dispersion-corrected density functional theory (DFT) methods. Several studies have employed different approaches to calculate the adsorption energy of small (and a few large) molecules in all-silica or protonated zeolites, often referencing high-level computational results or experimental data. However, systematic investigations into the adsorption of large pharmaceutical and personal care product (PPCP) contaminants in cation-exchanged zeolites remain limited. This study aims to determine which functional is particularly well-suited for large-scale screening of large PPCP adsorption in cation-exchanged zeolites. We have studied nine (mono- and divalent) metal cations (including alkali, alkaline earth, and transition metals) and compared 11 dispersion-corrected DFT approaches, including methods based on pairwise dispersion corrections, nonlocal van der Waals, and Minnesota density functionals. Furthermore, saturated cluster (SC) models are used to calculate DFT energies, which are then compared with the “gold standard” reference values from the DLPNO–CCSD(T) method. For periodic systems, the variation in adsorption energies for host–guest combinations is explained using cationic radii versus adsorption energy trends, with a few exceptions further clarified through charge density mapping, which identifies cases in which cation−π interactions are present. On the other hand, in SC models, various error statistics, along with the decomposition of total adsorption energies into electronic and dispersion contributions (for DFT) and Hartree–Fock and correlation energies (CCSD(T)), are applied to identify the most accurate functional for PPCPs@cation-FAU complexes. Overall calculations and error analysis provide a clear conclusion that the PBEsol-D3 functional can be recommended for the prediction of PPCP adsorption energies in cation-exchanged and all-silica zeolites.